Hours later, a boat with three fishermen was gnawed and circled for about three hours by a big shark about 15km west of Garden Island. Both incidents were just north of Port Kennedy, where a shark killed Brian Guest, 51, as he snorkelled within 30m of the beach on December 27. Mr Edwards said it was unlikely the sharks approached the boats on Saturday with the intention to attack.

Boat motors lured giant sharks off Rockingham: expert

11th May 2009, 6:00 WST

The big sharks which circled and gnawed two boats near Rockingham at the weekend were probably attracted by electrical signals from the motors and were not in attack mode, a shark expert claims.

Author and shark photographer Hugh Edwards said the beasts would probably have approached the boats out of curiosity after their acute senses picked up the pulses from the motors.

A Rockingham man aged 35 fell overboard as he tried to scare away a 4.5m white pointer after it nudged his boat about 7am near Point Peron.

Hours later, a boat with three fishermen was gnawed and circled for about three hours by a big shark about 15km west of Garden Island. Both incidents were just north of Port Kennedy, where a shark killed Brian Guest, 51, as he snorkelled within 30m of the beach on December 27. Mr Edwards said it was unlikely the sharks approached the boats on Saturday with the intention to attack.

“Sharks have sensors on their noses which pick up electrical pulses and motors on boats give that off so the sharks come in and have a look,” he said. “I’ve been out filming on boats lots of times and had sharks come up and nudge the boat a bit and have a bit of a nibble at the motor.

“Even when the man fell out of his boat, the shark just circled him instead of attacking so it obviously wasn’t interested in him.”

Fisheries Department senior research scientist Rory McAuley said it was highly unlikely the shark believed to have attacked Mr Guest was involved in either incident.

“Great white sharks are an extremely mobile species so they don’t spend more than a couple of days in one area before they move on to another area which could be hundred of kilometres away,” Dr McAuley said.

Perth beaches will be lined with tracking stations able to detect tagged white pointer sharks for a project that could help protect swimmers and determine whether sharks stalk coastal areas after developing a taste for human flesh.

The department and CSIRO researchers are installing 20 radio receivers, or “listening stations”, along patrolled beaches from Fremantle to Ocean Reef.

Dr McAuley said the new satellite receivers could pinpoint a tagged shark within a minute or two so patrol authorities could be told quickly if white pointers were swimming near popular beaches.